Apparatus and procedure for ultraviolet laser ablation

ABSTRACT

Apparatus for performing ultraviolet laser ablation of a surface, eg. an eye surface, including a laser delivery system ( 7 ) having a laser source ( 1 ) for generating a laser beam ( 2 ) and optics for applying the laser beam to the surface to be ablated, means ( 20, 20 ′) for providing a compatible liquid ( 32 ) in contact with the surface ( 4   a ) to be ablated, in a position whereby said laser beam ( 2 ) is applied to said surface through the liquid, wherein the laser beam is of a wavelength that substantially is not absorbed by the liquid.

FIELD OF THE INVENTION

[0001] This invention relates generally to ultraviolet laser ablation,used for example in laser eye treatment, and is of particular, though byno means exclusive, utility in ophthalmic refractive surgery operationssuch as laser in situ keratomiluesis (LASIK).

BACKGROUND ART

[0002] A number of refractive surgery operations involve the removal ofsmall amounts of corneal tissue to effect a refractive change. Inearlier developed laser operations such as photorefractive keratectomy(PRK), the epithelial layer is manually removed and then Bowman'smembrane and part of the stroma are ablated by laser energy. Thisoperation can lead to unwanted side effects, such as corneal haze, andis not suitable for higher refractive errors.

[0003] A more recently developed refractive operation called laser insitu keratomiluesis (LASIK) maintains the integrity of the epitheliallayer and Bowman's membrane. A flap of tissue is displaced from theanterior cornea and a minute amount of tissue in the shape of a lens isremoved from the stromal bed or from the underside of the lenticule, byway of laser ablation. The corneal lenticule or “flap” is then replacedto its original position creating an optical correction.

[0004] The LASIK refractive surgery procedure produces fewer sideeffects and quicker healing relative to PRK, as the epithelium andBowman's membrane are left intact. Because the epithelium is generallynot touched in LASIK, there is also less pain for the patient and thehealing process is enhanced with LASIK, presumably because the healingregion is protected: there is moreover only one type of tissue involvedin the healing process instead of two. It is thought that about 80% oflaser eye surgery is now LASIK rather than PRK.

[0005] Notwithstanding these advantages, a known problem with LASIK isthat the corneal surface formed by the microkeratome cut is relativelyrough and this reduces the patient's vision for watching the fixationlight, important for maintaining the pupil correctly aligned, andfurthermore reduces the vision of the eye tracker device used to guidethe laser delivery system. It is thought that these two issuescontribute to the known outcome that the statistical success rate ofLASIK is similar to PRK despite the enhanced healing process.

[0006] It is therefore an object of the invention, in a preferredapplication, to address the aforementioned problems with LASIK in aneffort to more consistently achieve the outcome expected of LASIKrelative to PRK. It is a more general object to provide an improvedultraviolet laser ablation procedure.

SUMMARY OF THE INVENTION

[0007] The invention involves recognition of the benefits of usingparticular wavelengths for the ablation, and of carrying out theablation in a manner which departs in one notable respect from theconventional approach.

[0008] The most commonly used wavelength in ultraviolet laser ablation,and in refractive laser surgery in particular, is 193 nm, the wavelengthof the pulsed beam derived from a conventional excimer laser. A problemissue with this wavelength has always been that it is very stronglyabsorbed by water and the presence of any stray fluid, including naturaleye tissue fluid, dramatically alters the ablation process. There istherefore a requirement to minimise liquid in the ablation region. Thus,physiological saline solution conventionally added to wash away the areain front of the eye before the treatment must be collected and extractedprior to the ablation, even though saline solution may be added againafterwards for washing purposes.

[0009] It has been appreciated by the present inventors that theabsorption by physiological saline solution of 193 nm laser light is sohigh as to be not accurately measurable using conventional varying depthmeasurements. The absorption of the 213 nm band is so low as to becapable of accurate measurement only with difficulty (ie. large columns(depths) of solution).

[0010] The invention entails the application of a physiologicallycompatible liquid in contact with the surface to be ablated, and the usefor the ablation of a laser beam of a wavelength that is substantiallynot absorbed by the liquid.

[0011] The invention provides apparatus for performing ultraviolet laserablation of a surface, eg. an eye surface, including a laser deliverysystem having a laser source for generating a laser beam and optics forapplying the laser beam to the surface to be ablated, means forproviding a compatible liquid in contact with the surface to be ablated,in a position whereby said laser beam is applied to said surface throughthe liquid, wherein the laser beam is of a wavelength that substantiallyis not absorbed by the liquid. In a first aspect of the invention, thelaser source is arranged to generate a laser beam at about 213 nm.

[0012] In a second aspect, the apparatus further includes cap or ringmeans for contacting the surface to be ablated to retain liquid withinthe cap means, which cap or ring means further includes overlying wallmeans spaced from the surface which has a lens through which theablating laser beam is directed.

[0013] In the first aspect, the invention also provides a method ofperforming ultraviolet laser ablation of a surface, eg. an eye surface,including having a compatible liquid in contact with the surface to beablated, and applying a laser beam to the surface through the liquid toeffect ablation of the surface with the laser beam, wherein the laserbeam is of a wavelength that substantially is not absorbed by theliquid, wherein said generated laser beam is at about 213 nm.

[0014] In a third aspect of the invention, there is provided a method ofperforming ultraviolet laser ablation of an eye surface including havingnatural liquid of the eye in contact with the eye surface to be ablated,and applying a laser beam to the eye surface through the liquid toeffect ablation of the surface with the laser beam, wherein the laserbeam is of a wavelength that substantially is not absorbed by theliquid.

[0015] The liquid may be provided by retaining the liquid in contactwith the surface to be ablated.

[0016] For laser ablation of an eye surface, the liquid is aphysiologically compatible liquid. In some aspects of the invention, thephysiologically compatible liquid retained in contact with the surfaceto be ablated is natural liquid of the eye. In other alternativeaspects, the liquid is introduced to the eye and the retaining means maythen include cap or ring means for contacting the surface to be ablatedto retain liquid within the cap means.

[0017] The laser beam may be produced from a solid state laser usingfrequency doubling and mixing crystals. A suitable arrangement,utilising a Q-switched neodymium: YAG laser as the primary source, isdescribed, for example in international patent publication WO 99/04317.

[0018] Where the liquid retaining means is a cap or ring device, itpreferably further includes overlying wall means spaced from the eyesurface which has a lens through which the ablating laser beam isdirected. The lens is preferably arranged to allow the patient to seethe fixation light in reasonable focus and to provide an even betteroptical surface to see with than the water alone.

[0019] The retaining means may include means for holding it against thesurface to be ablated. Such may be a suitable suction or vacuumarrangement.

[0020] In an advantageous application of the invention, the laserablation is a step in a LASIK procedure. For this purpose, the apparatusmay further include microkeratome means for cutting a flap from thecornea to expose an interior surface to be ablated. In this application,a common ring may serve as both the microkeratome guide ring and theliquid retaining means of the invention.

[0021] In a further aspect, the invention provides an apparatus forperforming ultraviolet LASIK on an eye surface, including a laserdelivery system having a laser source for generating a laser beam andoptics for applying the laser beam to the surface to be ablated, meansfor providing a compatible liquid in contact with the surface to beablated, in a position whereby said laser beam is applied to saidsurface through the liquid, wherein the laser beam is of a wavelengththat substantially is not absorbed by the liquid, and further includingmicrokeratome means for cutting a flap from the cornea to expose aninterior surface to be ablated and wherein a common ring serves as boththe microkeratome guide ring and means for retaining liquid in contactwith the surface to be ablated.

[0022] In a LASIK procedure, the method may further include cutting aflap from the cornea to expose an anterior surface to be ablated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The invention will be further described, by way of example only,with reference to the accompanying diagrams, in which:

[0024]FIG. 1 depicts an arrangement for performing LASIK according to afirst embodiment of the invention, shown at the point at which theliquid has been applied to the exposed corneal surface in preparationfor the ablation step;

[0025]FIG. 2 is a view similar to FIG. 1 of an alternative embodiment;

[0026]FIG. 3 is an enlargement of part of FIG. 2; and

[0027]FIG. 4 is a view similar to FIG. 3 showing a modified embodiment.

[0028] In the illustrated surgical laser system 100, a surgical lasersource 1, preferably a frequency converted solid state laser or anyother laser emitting a suitable wavelength as aforedescribed, eg. 213nm, directs a surgical laser beam 2, via delivery system 7, and lasermirror 3 (which is transparent to infra-red and visible light) towardsthe cornea of an eye 4 to be treated. To ensure that gross eye movementsare restricted, the patient's gaze is fixated on a flashing LED 5located beneath a surgical microscope 6 with which the surgeon views theprocedure. To compensate for decentration of the pupil through head, eyeor saccadic movement, or a loss of patient fixation, there is providedan eye tracking system generally indicated at 40. System 40 maytypically generate a collimated infra-red beam 8 which is directed viabeamsplitter 10 onto the optic axis of the eye coincident with mainlaser beam 2 and the fixation line of sight 9.

[0029] Laser source 1 may comprise a solid state laser and a pluralityof frequency doubling and mixing crystals for deriving the said laserbeam from the output beam of the laser. A suitable arrangement,utilising a Q-switched neodymium: YAG laser as the primary source, isdescribed, for example in international patent publication WO 99/04317.

[0030] A LASIK procedure has already commenced on eye 4 and amicrokeratome (not shown) has been utilised to part and draw back asurface flap 12 of the cornea, including the epithelium. In a firstembodiment depicted in FIG. 1, the operator now uses a supply tube 20 toapply and maintain a liquid layer 32 of physiologically compatiblesolution over exposed corneal surface 4 a. This is the inverse of theconventional step in excimer laser refractive surgery (at 193 nm) ofremoving the solution from in front of the corneal surface prior toablation. In the ablation step according to the invention, the ablatingbeam 8 is applied through liquid 32, to ablate surface 4 a. The beam isdimensioned by delivery system 7, and scanned in accordance with apredetermined control schedule in computer control 50, which alsomanages other components.

[0031] The physiologically compatible saline solution may typically bedextran, a fluid commonly used to avoid swelling of tissue, or balancedsalt solution.

[0032] The interposed retained liquid 32 helps cool the corneal tissuebecause there is substantially no absorption of the ablating light: theliquid remains cool and this helps reduce the limited degree of tissuedamage relative to the damage known to occur to a small degree inexcimer ablation.

[0033] A further advantage of the liquid overlay 32 is that there is nogas plume. The gas plume is the vaporised material produced by theablation which in conventional excimer ablation hovers over the ablatedsurface after each pulse and diminishes the effect of the nextsucceeding pulse in a non-uniform fashion, despite the application ofsuction to remove the plume. Some surgeons also suspect that the plumehas made them sick. To avoid the excessive build-up of ablation productsdissolved in the fluid, it is preferred that the fluid be replaced orflows over the ablation surface during the procedure.

[0034] Where the material to be ablated is not tissue there would besimilar advantages to do the ablation under a layer of water. Thisincludes the cooling effect of the fluid and the softening of theablation process that would help protect delicate structures ormaterials beneath the ablation site. One such non-tissue application isthe restoration of art works by laser ablation.

[0035] In alternative embodiments illustrated in FIGS. 2 and 3 and inFIG. 4, a cap or ring device 21 is positioned to confine and define theoverlying layer of liquid 32.

[0036] The cap or ring device 21 is generally cylindrical and is appliedto the exposed corneal surface 4 a by the operator once flap 12 has beenexcised and drawn aside. The cylindrical body 22 of the ring device isopen at its forward rim in contact with surface 4 a and, in the simpleembodiment shown in FIGS. 2 and 3, also open at its rear. Alternatively(FIG. 4), the ring 21′ may be closed at its rearward end by a wall 24including or consisting of a lens 26 pre-fitted within ring 20, orapplied in situ. Lens 26 preferably has an optically flat interior face28 as illustrated, though it could be convex or concave, and a convexexterior face 29.

[0037] Ring 20, 21′ defines a chamber 30 which is filled withphysiologically compatible saline solution 32, introduced, for example,through the tubes 33 (FIG. 4), which allow the fluid to flow over thesurface.

[0038] In the embodiment of FIG. 4, because of the interposed liquid 32,the presence of lens 30, and the fact that the refractive index ofcorneal tissue is similar to water, it is thought that the patient maybe able to see fixation light 5 more clearly, and thereby to maintain afixated gaze more reliably, while tracker system 40 is better able toclearly view the pupil.

[0039] Any other practical method of introducing the fluid to thesurface 4 a, eg a pipette, may of course be used.

1. (Amended) Apparatus for performing ultraviolet laser ablation of asurface, eg. an eye surface, including a laser delivery system having alaser source for generating a laser beam and optics for applying thelaser beam to the surface to be ablated, means for providing acompatible liquid in contact with the surface to be ablated, in aposition whereby said laser beam is applied to said surface through theliquid, wherein said laser source is arranged to generate said laserbeam at about 213 nm.
 2. (Cancelled)
 3. (Amended) Apparatus according toclaim 1 wherein said laser source includes a solid state laser and aplurality of frequency doubling and mixing crystals for deriving thesaid laser beam from the output beam of the laser.
 4. (Amended)Apparatus according to claim 1 or 3 further including means to retainsaid liquid in contact with the surface to be ablated.
 5. Apparatusaccording to claim 4 wherein said retaining means includes cap or ringmeans for contacting the surface to be ablated to retain liquid withinthe cap means.
 6. (Amended) Apparatus according to claim 5 wherein saidcap or ring means further includes overlying wall means spaced from thesurface which has a lens through which the ablating laser beam isdirected.
 7. Apparatus according to claim 4, 5 or 6 wherein saidretaining means includes means for holding it against the surface to beablated.
 8. Apparatus according to any one of claims 1 to 7 adaptedwhereby the laser ablation is a step in a LASIK procedure, and furtherincluding microkeratome means for cutting a flap from the cornea toexpose an interior surface to be ablated.
 9. (Amended) Apparatusaccording to claim 8 wherein a common ring serves both as a guide ringfor the microkeratome and as means for retaining liquid in contact withthe surface to be ablated.
 10. (Amended) A method of performingultraviolet laser ablation of an eye surface including having naturalliquid of the eye in contact with the eye surface to be ablated, andapplying a laser beam to the eye surface through the liquid to effectablation of the surface with the laser beam, wherein the laser beam isof a wavelength that substantially is not absorbed by the liquid. 11.(Cancelled)
 12. A method according to claim 10 or 11, wherein saidgenerated laser beam is at about 213 nm.
 13. (Amended) A methodaccording to claim 10 or 12, further including retaining said liquid incontact with the surface to be ablated.
 14. A method according to any ofclaims 10 to 13 applied to an eye, further including cutting a flap fromthe cornea to expose an anterior surface to be ablated.
 15. (New) Amethod of performing ultraviolet laser ablation of a surface includinghaving a compatible liquid in contact with the surface to be ablated,and applying a laser beam to the surface through the liquid to effectablation of the surface with the laser beam, wherein the laser beam isof a wavelength at about 213 nm.
 16. (New) A method according to claim15 wherein said liquid is a physiologically compatible liquid.
 17. (New)A method according to claim 15 or 16, further including retaining saidliquid in contact with the surface to be ablated.
 18. (New) A methodaccording to claim 15, 16 or 17 applied to an eye, further includingcutting a flap from the cornea to expose an anterior surface to beablated.
 19. (New) Apparatus for performing ultraviolet laser ablationof a surface, eg. an eye surface, including a laser delivery systemhaving a laser source for generating a laser beam and optics forapplying the laser beam to the surface to be ablated, means forproviding a compatible liquid in contact with the surface to be ablated,in a position whereby said laser beam is applied to said surface throughthe liquid, wherein the laser beam is of a wavelength that substantiallyis not absorbed by the liquid, further including cap or ring means forcontacting the surface to be ablated to retain liquid within the capmeans, which cap or ring means further includes overlying wall meansspaced from the surface which has a lens through which the ablatinglaser beam is directed.
 20. (New) Apparatus according to claim 19wherein said laser source is arranged to generate a laser beam at about213 nm.
 21. (New) Apparatus according to claim 19 or 20 wherein saidlaser source includes a solid state laser and a plurality of frequencydoubling and mixing crystals for deriving the said laser beam from theoutput beam of the laser.
 22. (New) Apparatus according to claim 19, 20or 21 wherein said cap or ring means includes means for holding itagainst the surface to be ablated.
 23. (New) Apparatus according to anyone of claims 19 to 22 adapted whereby the laser ablation is a step in aLASIK procedure, and further including microkeratome means for cutting aflap from the cornea to expose an interior surface to be ablated. 24.(New) Apparatus according to claim 23 wherein a common ring serves bothas a guide ring for the microkeratome and as means for retaining liquidin contact with the surface to be ablated.
 25. (New) Apparatus forperforming ultraviolet LASIK on an eye surface, including a laserdelivery system having a laser source for generating a laser beam andoptics for applying the laser beam to the surface to be ablated, meansfor providing a compatible liquid in contact with the surface to beablated, in a position whereby said laser beam is applied to saidsurface through the liquid, wherein the laser beam is of a wavelengththat substantially is not absorbed by the liquid, and further includingmicrokeratome means for cutting a flap from the cornea to expose aninterior surface to be ablated, wherein a common ring serves both as aguide ring for the microkeratome and as means for retaining liquid incontact with the surface to be ablated.
 26. (New) Apparatus according toclaim 25 wherein said laser source is arranged to generate a laser beamat about 213 nm.
 27. (New) Apparatus according to claim 25 or 26 whereinsaid laser source includes a solid state laser and a plurality offrequency doubling and mixing crystals for deriving the said laser beamfrom the output beam of the laser.